1. Field of the Invention
The present invention relates to a toner hopper which is capable of supplying toner to a developing unit through the effect of the rotation of a stirring roller and a feeding roller and is used in an image forming apparatus such as a copying machine for forming an image by means of an electrophotographic technique.
2. Description of the Related Art
The inventors of the present application know an image forming apparatus in which a toner hopper is attachable to a developing unit providing a magnet roller and a stirring roller for a developing agent. The toner hopper serves to feed a necessary amount of toner to a photosensitive drum of the developing unit. In the known image forming apparatus, after all the toner stored in the toner hopper is consumed by feeding it to the developing unit, it is necessary to attach a new toner hopper. Hence, to extend the operating period of the toner hopper, recently, the toner hopper having a larger toner capacity has been under study.
In such a large-capacity toner hopper, the toner is stored in the toner hopper for a relatively long time. Hence, a stirring roller is provided in the toner hopper for making the toner uniform and feeding of the toner to the developing unit easier.
The stirring roller is driven by a motor and transmits its force of rotation to a feeding roller through the effect of an interlocking mechanism composed of gear trains. The stirring roller is rotated as being interlocked with the feeding roller.
In the known toner hopper described above, the stirring roller is constantly interlocked with the feeding roller through the effect of the gear mechanism. Hence, the distance between toner particles stored in the toner hopper are stuck together so that the particle density of the toner is made larger, resulting in fixing toner particles. This is due to the vibration taking place when the toner hopper is in transportation and the adverse effect of the long-term storage of the toner in the toner hopper. Immediately after attaching the toner hopper to the developing unit, the fixed toner particles need the driving means (motor) to supply more force of rotation to the feeding roller and the stirring roller. This results in disabling to rotate the stirring roller and the feeding roller and often causing the driving means to be in trouble.
To overcome the shortcomings, it is necessary to provide a driving means for producing larger force of rotation. However, it brings about the other disadvantages, that is, the enlargement and the cost-up of the device itself.